The city of Boston’s pension plan reported a 1.1 percent loss on its investments for 2015, ranking it 99th out of 105 public retirement systems in the Commonwealth for the year, according to a report by the Boston Municipal Research Bureau.

The investment return compared with a 1.1 percent gain for the Massachusetts state pension fund. The average return for systems across the state was 0.9 percent, according to the state pension watchdog, the Public Employee Retirement Administration Commission.

While the Boston Retirement System’s returns have lagged, the $4 billion fund is still healthier, at 70.2 percent funded, than many public pensions. It remains on schedule to be fully funded by 2025, according to the research bureau, well before the state’s 2036 deadline.

The Boston fund has underperformed the state fund over one, five and 31 years. Over 10 years, Boston has produced a nearly 6 percent return annually, while the state Pension Reserves Investment Trust returned 5.9 percent, according to the research bureau report.

Boston’s assumed annual rate of return is 7.75 percent; over time, if it earns less than that annually, the fund will require larger contributions to make up the difference.

Beth Healy can be reached at beth.healy@globe.com. Follow her on Twitter @HealyBeth.